> every Meteor app already has an API :) Your Meteor client can connect to any other Meteor server by calling Meteor.connect()

What about a non-Meteor client connecting to a Meteor server? Does that client have to understand DDP, or is that what you mean by "we could map DDP to REST" - there's no support for non-DDP clients now, but it's planned?

The latency compensation and Meteor.call() interface sound great, but what I understood by the GP's question about an API was "how can other clients besides mine talk to my app?".